The present invention relates to a method for manufacturing ceramic tooth restorations comprising a connecting element which is inserted in recesses of two tooth replacement elements such as crowns or bridge members neighboring each other. The present invention also relates to a method for manufacturing such a ceramic tooth restoration.
A tooth restoration of the aforementioned kind is known from U.S. Pat. No. 4,744,757. In this tooth restoration, a connecting element is inserted into recesses of two neighboring bridge members, as shown in FIG. 3 of the patent. It is still possible to move the tooth restoration before it is finally fixed in its position. For accomplishing this, a bonding agent or tooth cement is used which hardens after the solvents contained therein evaporate. Alternatively, light-curable resins can be used, in which case it is assumed that the ceramic materials used for the manufacture of tooth restorations are sufficiently light-penetrable in the spectrally important UV-range in order to ensure a secure light-curing result.
A disadvantage of this solution, however, is that the curing degree depends on the ceramic material used. For safety reasons, the tooth restoration should only be made out of a glass ceramic material that is especially easily penetrated by light.
The tooth restorations manufactured according to that method have proven to be not particularly durable. In particular, where dental cements have been used, cracks occurred which are perhaps traceable to non-compatible thermal extension coefficients.
In contrast thereto, it is an object of the present invention to create a tooth restoration comprising a connecting element which is inserted in recesses of two tooth replacement elements (crowns or bridge members) neighboring each other and a method for manufacturing such a tooth restoration so as to provide a long-term stable and reliable connection between crowns or bridge members without negatively affecting the free adjustability thereof.
This object is solved with the inventive ceramic tooth restoration by sintering the connecting element into the recesses at temperatures below approximately 800xc2x0 C. by means of a glass powder paste or glass powder slurry.
Surprisingly, the inventive sintering process of the connecting elements by means of glass powder pastes or glass powder slurries (in the following the term glass paste will be used for both the glass powder paste and the glass powder slurry) results in a durable tooth restoration which especially is not prone to the formation of cracks. The glass materials used for the sintering process can be selected easily such that their thermal extension coefficients lie at least in the vicinity of those of the ceramic material used. When, for example, a lithium disilicate ceramic is used with a thermal extension coefficient of 10.8xc3x9710xe2x88x926/K, a lithium disilicate glass material can be used without a problem as a sintering material. By baking the connecting elements into the crowns or bridges, a particularly well reinforced connection is created. By selecting the baking temperature appropriately, it can be ensured that the ceramic material itself does not lose its hardness. Temperatures in the range of between 600xc2x0 and 800xc2x0 C. are preferred for the sintering process.
According to the current restoration technologies, full ceramic bridge reconstructions have to be manufactured anew if there are fitting problems because no adequate ceramic bonding technique exists. According to the present invention a repeated manufacture of the cost-intensive full-ceramic restoration becomes obsolete and, furthermore, it does not require any plastic patching.
According to a particularly favorable aspect of the invention, a stable and durable bridge can also be manufactured when the side walls of the tooth restoration are relatively thin. In this case the inventive connecting element is positioned in the area of the grinding surface and is practically inserted from above as a small plate and is fired subsequently. It is understood that the selection of the length and measurements of the connecting element can be adjusted to the requirements in a wide range.
Also, the shape and design of the connecting element can be largely adjusted to the requirements. In particular, if the connecting element extends in the area of the grinding surfaces, an oblong and flat design can offer an especially stable connection. Instead of pin-shaped connecting elements, bone-shaped connecting elements can also be inserted whereby in each case play or a spacing is provided between the recesses and the connecting element so that the glass paste can be received.
The recess oversize relative to the connecting elements can be largely adjusted as required. It is possible, for example, to provide a gap of, e.g. {fraction (1/10)} of the thickness of the connecting element and entirely fill this gap with glass-sintering material.
The filling can be performed such that the recesses are filled with glass paste, or, preferably, by immersing the connecting elements in the glass paste and, subsequently, inserting them into the recesses of the crown or bridge members.
Subsequent to the insertion, the bridge or crown is introduced into the model or into the mouth of the patient and the correct positioning is defined. Subsequently, the geometry is stabilized by suitable mechanical procedures, e.g., by clamps, fixing gypsum, or plastic, and the thus prepared tooth restoration is post-sintered in a short firing process so that the connecting elements become securely anchored within the recesses and a connection of long term stability is ensured.
The object and advantages of the present invention will appear more clearly from the following specification in conjunction with the accompanying schematic drawings in which preferred embodiments of this invention are illustrated.